Background The shape of the corpus callosum may differ in schizophrenia, although no study has compared first-episode with established illness. Aims To investigate the size and shape of the corpus callosum in a large sample of people with first-episode and established schizophrenia. Method Callosal size and shape were determined using highresolution magnetic resonance imaging on 76 patients with first-episode schizophrenia-spectrum disorders, 86 patients with established schizophrenia and 55 healthy participants. Results There were no significant differences in total area across groups. Reductions in callosal width were seen in the region of the anterior genu in first-episode disorder (P<0.005). Similar reductions were seen in the chronic schizophrenia group in the anterior genu, but also in the posterior genu and isthmus (P = 0.0005). Conclusions Reductions in anterior callosal regions connecting frontal cortex are present at the onset of schizophrenia, and in established illness are accompanied by changes in other regions of the callosum connecting cingulate, temporal and parietal cortices.